I have a friend I know I’ll be hearing from once he reads that title. For him and others who enjoy poking fun at the solar system’s seventh planet, here’s a selection of Uranus jokes. Now for some great news. If you’d like to see Uranus this week, Mars will get you there. The Red Planet is approaching the “other blue planet” and will skim less than 1° north of it when the two are in conjunction on Tuesday, Feb. 12.
But don’t wait that long. Tonight, they’ll be just shy of 3° apart and easily fit in the field of view of any pair of binoculars. Then over the next few nights you can watch Mars approach the more distant planet until conjunction and beyond if you like. Mars shines at 1st magnitude and can’t be missed. It’s the only bright “star” shining high in the western sky at dusk. And you can’t mistake its orange color. The moon glides 6° south of the planet (equal to three fingers held together at arm’s length against the sky) on Sunday, Feb. 10.
Uranus glows at magnitude 5.8, right around the naked-eye limit from the countryside. The moon is thickening though and relatively nearby, so you’ll definitely need binoculars. Just point them at the Red Planet and use the map to locate Uranus. Because of its great distance, Uranus looks exactly like a star in binoculars. A small telescope magnifying around 100x will show it as a tiny disk. The blue planet, colored so by methane in its atmosphere, lies 1.9 billion miles (3 billion km) from the Earth this week or nearly 13 times farther than Mars.
Like Mars, Uranus is also moving along its orbit but so much more slowly that it’s almost stationary in the sky compared to speedy Mars. Even in large telescopes the planet doesn’t much different from a featureless blue cue ball. But not always. Belts and storms have been recorded there, and since 1990, the Hubble Space Telescope has kept a yearly watch on both Uranus and the other ice-giant planet, Neptune. Astronomers monitor the weather and long-term seasonal changes at these distant worlds.
Photos taken last fall have revealed a vast, bright cap of clouds over Uranus’s polar regions which may form due to changes in atmospheric flows brought on by the changing seasons. The cap is much more prominent compared to its appearance in 1986 during the Voyager 2 flyby. Hard to believe, but even at that distance there are seasons.
Recall that the planet’s axis is tilted 98°, so it’s basically spinning on its side.The north pole faces the sun for a quarter of its orbit (21 years); half an orbit later, it’s plunged into darkness for 21 years. Right now, Uranus is coming up on the middle of its summer season when the sun shines almost directly down on the north pole and never sets. When Voyager 2 snapped closeups 33 years ago, it was only just emerging from a long, dark winter. No wonder we’re seeing cloud changes.
The Hubble photo also shows a large, compact methane-ice cloud along the edge of the polar cap, a feature bright enough to show in photos taken by amateur astronomers, and a narrow cloud belt north of the equator. Scientists are still mystified how such narrow bands form on a planet with broad, westward-blowing wind jets. Uranus has no solid surface. Its atmosphere of hydrogen and helium surrounds a slushy-icy, water-rich interior with a possible rocky core at the center of it all.
So go ahead and get those binoculars pointed for a look at this marvel. Look more than once, and you’ll see how quickly Mars moves across the sky.